Question: How do you set up a MongoDB cluster on Ubuntu?

Answer

Setting up a MongoDB cluster, also known as a Replica Set, on Ubuntu involves several steps that ensure redundancy and high availability of your database. Below is a comprehensive guide to achieve this setup.

Prerequisites

• Three or more Ubuntu servers (version 18.04 or later) for the members of the replica set.
• Sudo privileges on each server.

Step 1: Install MongoDB

On all your Ubuntu servers, install MongoDB. MongoDB's official package provides the most up-to-date version and is recommended over the default Ubuntu packages.

1. Import the MongoDB public GPG key:

wget -qO - https://www.mongodb.org/static/pgp/server-4.4.asc | sudo apt-key add -

2. Create a list file for MongoDB:

echo \"deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu $(lsb_release -sc)/mongodb-org/4.4 multiverse\" | sudo tee /etc/apt/sources.list.d/mongodb-org-4.4.list

3. Update the local package database:

sudo apt-get update

4. Install MongoDB:

sudo apt-get install -y mongodb-org

Repeat these steps on all the servers.

Step 2: Configure the MongoDB Replica Set

On each server, edit the MongoDB configuration file, /etc/mongod.conf, to enable replication and specify the replica set name.

1. Open the configuration file:

sudo nano /etc/mongod.conf

2. In the net section, uncomment the bindIp line and replace 127.0.0.1 with 0.0.0.0 to allow connections from other servers.

3. In the replication section, add:

replication:
  replSetName: \"rs0\"

Here, rs0 is the name of the replica set. You can choose any name you prefer.

4. Restart MongoDB to apply the changes:

sudo systemctl restart mongod

Step 3: Initialize the Replica Set

Choose one server to act as the primary node and connect to the MongoDB shell on that server:

mongo

In the Mongo shell, initialize the replica set:

rs.initiate()

After initiation, add the other servers as members of the replica set:

rs.add(\"server2_ip:27017\")
rs.add(\"server3_ip:27017\")

Replace server2_ip and server3_ip with the actual IP addresses of your other servers.

Step 4: Verify the Replica Set Configuration

To verify that the replica set has been configured correctly, use the following command in the Mongo shell:

rs.status()

This command will display the status of the replica set, including the primary and secondary nodes.

Conclusion

You have now successfully set up a MongoDB replica set on Ubuntu. This setup ensures that your MongoDB deployment is highly available and can withstand server failures.